1. Field
The disclosure relates to current sensing in electronic circuitry, and in particular, to sensing current flow delivered to a load.
2. Background
Cellular phones and other portable consumer devices commonly incorporate one or more speakers to generate audio output, such as voice, for a user. Class D speaker drivers are typically used to deliver maximum power to the speakers. The miniature speakers used in such portable devices are generally not robust, and may readily fail when, e.g., operated outside of a pre-specified temperature range. To prevent over-heating of a speaker, circuitry may be provided to measure the operating current through the speaker, or more generally, the load. The temperature of the speaker may then be estimated by taking into account both the measured operating current and the speaker impedance, and appropriate measures may be taken when the temperature falls outside the allowable range.
To monitor the operating current, one or more external sense resistors may be placed in series with the load, and the voltage across such sense resistors may in turn be detected, e.g., by a voltage amplifier. Sensing the voltage across the sense resistors may be complicated when the signal voltages used to drive the speaker are switched on and off over multiple phases of a cycle, for example, according to a Class D amplifier scheme. During one or more of such multiple phases, the current flowing through the load may not correspond to the current flowing through the sense resistors. To accurately measure speaker current, it is necessary to account for such multiple phases when measuring the sense resistor voltages.
It would be desirable to provide simple and robust techniques for sensing load current that can accommodate loads driven by multi-phase driving voltages or other types of driving voltages.